JP6752750B2 - Decontamination treatment water treatment method - Google Patents

Description

The present disclosure relates to a decontamination treated water treatment method.

In a nuclear power plant or the like, when radioactive substances adhere to the members constituting the plant equipment, chemical decontamination may be performed to remove the radioactive substances from the members.
For example, Patent Document 1 discloses a method for eluting and removing a radioactive substance from a decontamination object to which an oxide film containing a radioactive substance is attached, using an oxidizing agent or the like. In this method, the object to be decontaminated is immersed in treated water to which permanganic acid is added as an oxidizing agent, a radioactive substance is eluted together with the components contained in the oxide film, and then the treated water is brought into contact with an ion exchange resin. Then, the radioactive substance contained in the treated water is adsorbed on the ion exchange resin and removed.
Further, in Patent Document 1, in order to remove the oxidizing agent from the treated water, a reducing agent is added to the treated water after eluting the radioactive substance as described above, and precipitation is caused by the reaction between the oxidizing agent and the reducing agent. It is disclosed that the precipitate is removed from the treated water after the product is produced.

Japanese Unexamined Patent Publication No. 2014-92442

By the way, if the treated water used for chemical decontamination of a plant or the like contains an oxidizing agent, the plant equipment immersed in the treated water may be corroded by the oxidizing agent, which may affect the plant equipment. .. It is necessary to inject pure water in order to suppress such effects on plant equipment. Since pure water is injected, excess water containing an oxidizing agent is generated.
The oxidizing agent in the treated water can be removed as a precipitate by adding a reducing agent to the treated water containing the oxidizing agent to form a precipitate, for example, as described in Patent Document 1. However, the precipitate formed by the reaction of the oxidizing agent and the reducing agent may have low fluidity, and in this case, the sediment may block the pipes and equipment constituting the plant.
In this regard, Patent Document 1 does not specifically disclose a measure for suppressing clogging of the equipment due to the precipitate generated when the oxidizing agent is removed from the treated water.

In view of the above circumstances, at least one embodiment of the present invention aims to provide a method for treating decontaminated water that can suppress clogging of pipes and equipment.

(1) The decontamination-treated water treatment method according to at least one embodiment of the present invention is
An oxidation step in which a decontamination object to which a metal oxide is attached is immersed in treated water containing permanganate ions derived from an oxidizing agent to elute the metal elements constituting the metal oxide into the treated water.
A pH adjusting step of adding a pH adjusting agent to the treated water to adjust the pH of the treated water to 7 or more and 13 or less.
A first reducing step of adding a first reducing agent to the treated water after the pH adjusting step to reduce the permanganate ions contained in the treated water, and a first reducing step.
To be equipped.

As a result of diligent studies by the present inventors, when the treated water containing permanganate ions is acidic, when a reducing agent is added to the treated water, the reaction between the permanganate ions contained in the treated water and the reducing agent causes. It was clarified that the fluidity of the produced precipitate was relatively low, while the fluidity of the similarly produced precipitate was relatively high when the pH of the treated water containing permanganate ions was relatively high.
In this regard, according to the method (1) above, after elution of metal elements from the decontamination target with permanganate ions, the pH of the treated water containing permanganate ions is adjusted to 7 or more and 13 or less. Therefore, since the permanganate ion in the treated water is reduced, the reaction between the permanganate ion and the reducing agent facilitates the formation of a precipitate having relatively high fluidity. Therefore, it is possible to suppress clogging of pipes and equipment (for example, clogging of an evaporator used in a concentration step described later) due to a precipitate generated by a reaction between permanganate ions and a reducing agent.

(2) In some embodiments, the method (1) further comprises a heating step of heating the treated water after the first reduction step.

According to the method (2) above, by heating the treated water after the first reduction step, the fluidity of the precipitate generated by the reaction between the permanganate ion and the reducing agent can be further enhanced. Therefore, it is possible to effectively suppress blockage of piping and equipment caused by sediment.

(3) In some embodiments, the method (1) or (2) further comprises a concentration step of concentrating the treated water after the first reduction step.

According to the method (3) above, the treated water after the first reduction step is concentrated to maintain a relatively high fluidity of the precipitate even when the concentration of the precipitate in the treated water is high. It is possible to suppress blockage of piping and equipment due to sedimentation.

(4) In some embodiments, in the method (3) above, the concentration step includes the heating step.

According to the method (4) above, since the heating step is performed as the concentration step for concentrating the treated water, the treatment efficiency of the treated water can be improved.

(5) In some embodiments, in any of the methods (1) to (4) above, the pH of the treated water is adjusted to 10 or more and 12 or less in the pH adjusting step.

According to the method (5) above, the pH of the treated water containing permanganate ions is adjusted to 10 or more and 12 or less in the pH adjustment step, and then the permanganate ions in the treated water are reduced. The reaction between the ions and the reducing agent makes it easier to form a precipitate with relatively high fluidity. Therefore, it is possible to effectively suppress blockage of pipes and equipment caused by a precipitate generated by the reaction between permanganate ions and a reducing agent.

(6) In some embodiments, in any of the methods (1) to (5) above, the oxidizing agent comprises potassium permanganate.

According to the method (6) above, by immersing the decontamination target in treated water to which potassium permanganate has been added as an oxidizing agent, a metal element constituting a metal oxide adhering to the decontamination target ( For example, chromium) can be effectively eluted in the treated water.

(7) In some embodiments, in the methods (1) to (6) above, the pH adjuster comprises at least one alkali metal hydroxide.

According to the method (7) above, since an alkali metal hydroxide which is a strongly basic compound is used as a pH adjuster, the treated water is treated even when the pH of the treated water before pH adjustment is relatively low. It is easy to adjust the pH of 7 or more and 13 or less.

(8) In some embodiments, in any of the methods (1) to (7) above, the first reducing agent comprises at least one of hydrogen sulfite, sulfite or hydrazine.

According to the method (8) above, since at least one of sodium bisulfite or hydrazine is used as the first reducing agent, permanganate ions in the treated water are generated under the condition that the pH of the treated water is 7 or more and 13 or less. It can be reduced appropriately.

(9) In some embodiments, in any of the methods (1) to (8) above,
In the first reducing step, the first reducing agent having 1.1 molar equivalents or more and 1.3 molar equivalents or less is added to the treated water with respect to the oxidizing agent.

According to the method (9) above, since 1.1 mol equivalent or more of the first reducing agent is added to the treated water with respect to the oxidizing agent, a part of the first reducing agent is used by the oxygen dissolved in the treated water. Is consumed, the permanganate ion derived from the oxidizing agent can be appropriately reduced. Further, according to the method (9) above, since the first reducing agent having 1.3 molar equivalents or less with respect to the oxidizing agent is added to the treated water, the cost increase due to the increase in the amount of the first reducing agent used is suppressed. be able to.

(10) In some embodiments, the method of any of (1) to (9) above is
A second reducing step is further provided in which a second reducing agent is added to the treated water after the pH adjusting step to reduce the metal element dissolved in the treated water.

According to the method (10) above, a second reducing agent can be added to the treated water after the pH adjustment step to reduce the metal element dissolved in the treated water and convert it into another form. .. For example, by reducing hexavalent chromium dissolved in the treated water to trivalent chromium with a second reducing agent, the treated water can be made easier to handle.

(11) In some embodiments, in the method (10) above,
In the second reducing step, a second reducing agent having 1.0 molar equivalent or more and 2.0 molar equivalent or less is added to the treated water with respect to the oxidizing agent.

According to the method (11) above, 1.0 molar equivalent or more of the second reducing agent is added to the treated water with respect to the oxidizing agent, so that the metal element dissolved in the treated water can be appropriately reduced. it can. Further, according to the method (11) above, since the second reducing agent having 2.0 molar equivalents or less with respect to the oxidizing agent is added to the treated water, the cost increase due to the increase in the amount of the second reducing agent used is suppressed. be able to.

According to at least one embodiment of the present invention, there is provided a method for treating decontaminated water that can suppress clogging of pipes and equipment.

It is a schematic block diagram of the nuclear power plant which concerns on one Embodiment. It is a flowchart of the treated water treatment method which concerns on one Embodiment.

Hereinafter, some embodiments of the present invention will be described with reference to the accompanying drawings. However, the dimensions, materials, shapes, relative arrangements, etc. of the components described as embodiments or shown in the drawings are not intended to limit the scope of the present invention to this, and are merely explanatory examples. Absent.

The treated water treatment method according to some embodiments is a method of treating treated water for chemically decontaminating plant equipment components to which radioactive substances are attached in a nuclear power plant. First, a nuclear power plant to which the treated water treatment method according to some embodiments is applied will be described.

FIG. 1 is a schematic configuration diagram of a nuclear power plant according to an embodiment. As shown in FIG. 1, the nuclear plant 1 includes a nuclear reactor 2 for generating steam by thermal energy generated in a fission reaction, a steam turbine 4 driven by the steam generated in the nuclear reactor 2, and a steam turbine. A generator 6 driven by the rotation of the rotating shaft of 4 is provided. The nuclear reactor 2 shown in FIG. 1 is a pressurized water reactor (PWR: Pressurized Water Reactor). In other embodiments, the reactor 2 may be a boiling water reactor (BWR), or unlike a light water reactor including a pressurized water reactor and a boiling water reactor, a speed reducer or It may be a type of nuclear reactor that uses a substance other than light water as a cooling material.

The reactor 2 includes a primary cooling loop 10 through which primary cooling water (primary coolant) flows, a reactor vessel (pressure vessel) 11, a pressurizer 14, a steam generator 16, and a primary coolant pump provided in the primary cooling loop 10. (Coolant pump) 18 and the like. The primary coolant pump 18 is configured to circulate the primary cooling water in the primary cooling loop 10. Further, the pressurizer 14 is configured to pressurize the primary cooling water in the primary cooling loop 10 so that the primary cooling water does not boil. The reactor vessel 11, the pressurizer 14, the steam generator 16, and the primary coolant pump 18 constituting the reactor 2 are stored in the reactor containment vessel 19.
The reactor vessel 11 contains fuel rods 12 containing pelletized nuclear fuel (for example, uranium fuel, MOX fuel, etc.), and the thermal energy generated by the fission reaction of this fuel causes the primary in the reactor vessel 11 to be contained. The cooling water is heated. The reactor vessel 11 is provided with control rods 13 for absorbing and adjusting the number of neutrons generated in the core including nuclear fuel in order to control the reactor output. The primary cooling water heated in the reactor vessel 11 is sent to the steam generator 16 and heats the secondary cooling water (secondary coolant) flowing through the secondary cooling loop 20 by heat exchange to generate steam.

The steam generated in the steam generator 16 is sent to the steam turbine 4 including the high-pressure turbine 21 and the low-pressure turbine 22 to rotationally drive the steam turbine 4. Further, the steam turbine 4 is connected to the generator 6 via a rotating shaft, and the generator 6 is driven by the rotation of the rotating shaft to generate electric energy. A moisture separation heater 23 is provided between the high-pressure turbine 21 and the low-pressure turbine 22, and the steam after working in the high-pressure turbine 21 is reheated and then sent to the low-pressure turbine 22. ing.

The secondary cooling loop 20 is provided with a condenser 24 and a heater (not shown), and steam after working in the low-pressure turbine 22 is condensed and heated in the process of passing through the condenser 24 and the heater. It is designed to return to the steam generator 16. The secondary cooling loop 20 is provided with pumps such as a condensate pump 25, and these pumps circulate the secondary cooling water in the secondary cooling loop 20. Further, cooling water (for example, seawater) for cooling steam from the low-pressure turbine 22 by heat exchange is supplied to the condenser 24 via a pump 15.

The treated water treatment method according to some embodiments is applied to the decontaminated treated water for chemically decontaminating the primary cooling system through which the primary coolant flows in the nuclear power plant 1 having the above configuration.
The surface of the equipment that comes into contact with the primary coolant in the primary cooling system, that is, the surface of the members that make up the equipment such as the reactor vessel 11, the pressurizer 14, the steam generator 16, or the primary coolant pump 18 provided on the primary cooling loop 10. An oxide film containing a radioactive substance (for example, a metal oxide such as chromium, iron, or nickel) may adhere to the surface due to factors such as metal corrosion. The treatment method according to some embodiments can be applied to the treatment of excess water (treated water) used when chemically decontaminating the above-mentioned member (decontamination target object).

Next, the treated water treatment method according to some embodiments will be described as an example when applied to the above-mentioned nuclear power plant 1.
FIG. 2 is a flowchart of a treated water treatment method according to an embodiment. As shown in the flowchart of FIG. 2, the treated water treatment method according to the embodiment includes an oxidation step S2, a pH adjustment step S4, a first reduction step S6, a second reduction step S8, and a heating step S10. The concentration step S12 is provided.
In some embodiments, the second reduction step S8, the heating step S10, and the concentration step S12 do not necessarily have to be performed, and these steps may be performed as needed.

(Oxidation process)
First, in the oxidation step S2, the object to be decontaminated to which the metal oxide is attached is immersed in treated water containing permanganate ions derived from an oxidizing agent, and the metal elements constituting the metal oxide are eluted in the treated water. Let me.
For example, treated water to which an oxidant has been added is introduced into the primary cooling loop 10, and decontamination objects (for example, reactor vessel 11, pressurizer 14, steam) to which an oxide film (metal oxide) containing a radioactive substance is attached. The generator 16 or the primary coolant pump 18) may be immersed in the treated water.

The treated water used in the oxidation step S2 may be an aqueous solution of an oxidizing agent.

Oxidizing agent used in the oxidation step S2 is permanganate ion ^- is intended to include (MnO _4). The cation constituting the oxidizing agent together with the permanganate ion may be, for example, a hydrogen ion (H ⁺ ) or an alkali metal ion such as potassium. The oxidizing agent may be, for example, a permanganate such as potassium permanganate, or a permanganate. By using treated water containing permanganate ions, metal oxides (for example, oxides of chromium, iron, nickel, etc.) adhering to the decontamination target can be effectively eluted.
For example, in the oxidation step S2, by oxidizing water-insoluble chromium oxide contained in the oxide film (metal oxide) to (III) by permanganate ions in the treated water, a water soluble hexavalent chromium (HCrO ₄ ^- or as CrO ₄ ^2-like), can be eluted with radioactive material adhering to the oxide film.

In the oxidation step S2, the primary coolant pump 18 may be used to circulate the treated water containing an oxidizing agent (permanganate ion). In this case, the primary coolant pump 18 is operated while supplying water (pure water or the like) to the primary coolant pump 18 so that the chemicals such as the oxidant contained in the coolant do not come into contact with the primary coolant pump 18. You may.

The steps described below (steps after the pH adjusting step S4) may be carried out on the treated water in a state where the decontamination target is immersed in the primary cooling loop 10 after the oxidation step S2 is executed. After executing the oxidation step S2, it may be carried out on the treated water discharged from the primary cooling loop 10 (for example, the treated water stored in a tank or the like).

(PH adjustment process)
In the pH adjusting step S4, a pH adjusting agent is added to the treated water after the oxidation step S2 is executed to adjust the pH of the treated water to 7 or more and 13 or less. In some embodiments, in the pH adjusting step S4, a pH adjusting agent may be added to the treated water after the oxidation step S2 to adjust the pH of the treated water to 10 or more and 12 or less.

The pH adjusting agent used in the pH adjusting step S4 may contain at least one alkali metal hydroxide. The alkali metal oxide may be sodium hydroxide, lithium hydroxide or potassium hydroxide. By using an alkali metal hydroxide which is a strongly basic compound as a pH adjuster, the pH of the treated water is 7 or more and 13 or less or 10 or more even when the pH of the treated water before the pH adjustment is relatively low. Easy to adjust to 12 or less.

(First reduction step)
In the first reduction step S6, the first reducing agent is added to the treated water after the pH adjustment step S4 is executed to reduce the permanganate ions contained in the treated water.

In the oxidation step S2 that oxidizes the metal oxide adhering to the decontamination target, the entire amount of permanganate ions (oxidizer) contained in the treated water is not used up, and the excess permanganate ions are treated even after the oxidation step S2. It may remain in the water. In this case, the treated water after performing the oxidation step S2 and the pH adjusting step S4 contains permanganate ions. As described above, if permanganate ions remain in the treated water, it may affect these devices, such as oxidizing the constituent materials of the devices that come into contact with the treated water. Therefore, by reducing the permanganate ion in the treated water in the first reduction step S6, the oxidizing power of the treated water can be reduced and the influence on the equipment in contact with the treated water can be suppressed.

Here, according to the findings of the present inventors, when the treated water after executing the oxidation step S2 is acidic, if a reducing agent is added to the treated water without performing the pH adjusting step S4, the treated water becomes The reaction between the contained permanganate ion and the reducing agent produces a low-fluidity precipitate such as manganese dioxide. The half-reaction formula in which manganese dioxide is produced by reducing permanganate ions is represented by the following formula (A).
MnO ₄ ⁻ + 4H ⁺ + 3e ⁻ → MnO ₂ + 2H ₂ O… (A)
On the other hand, when the pH of the treated water after executing the oxidation step S2 is adjusted to a relatively large value (for example, alkaline) and then a reducing agent is added to the treated water, the permanganic acid contained in the treated water is contained. Depending on the reaction between the ion and the reducing agent, for example, manganese hydroxide (Mn (OH) ₂ ), manganese oxide (II, III) (Mn ₂ O ₃ ), manganese oxide (III) (Mn ₂ O ₃ ), etc. A relatively fluid deposit is produced. The half-reaction formula in which manganese hydroxide is produced by reducing permanganate ions is represented by the following formula (B).
MnO ₄ ⁻ + 6H ⁺ + 5e ⁻ → Mn (OH) ₂ + 4H ₂ O… (B)

Therefore, as in the above-described embodiment, the pH of the treated water is adjusted to 7 or more and 13 or less or 10 or more and 12 or less in the pH adjusting step S4, and then the permanganate ion in the treated water is adjusted in the first reduction step S6. By reducing the pH, the reaction between the permanganate ion and the reducing agent facilitates the formation of a precipitate having relatively high fluidity. Therefore, it is possible to suppress clogging of pipes and equipment (for example, clogging of the evaporator used in the concentration step S12 described later) due to the precipitate generated by the reaction between the permanganate ion and the reducing agent.

The first reducing agent used in the first reducing step S6 is, for example, hydrogen sulfite (for example, sodium hydrogen sulfite (NaHSO ₃ ) or the like), sulfite (for example, sodium sulfite (Na ₂ SO ₃ ) or the like), or hydrazine (. It may contain at least one of N ₂ H ₄ ).
In this case, the permanganate ion in the treated water can be appropriately reduced under the condition that the pH of the treated water is 7 or more and 13 or less or 10 or more and 12 or less.
The half-reaction formula when sulfite (sulfite ion) is used as a reducing agent is represented by the following formula (C).
SO ₃ ^2- + H ₂ O → SO ₄ ^2- + 2H ⁺ + 2e ⁻ … (C)

The amount of the first reducing agent added in the first reducing step S6 may be 1.1 molar equivalents or more and 1.3 molar equivalents or less with respect to the oxidizing agent used in the oxidizing step S2.
When 1.1 mol equivalent or more of the first reducing agent is added to the treated water with respect to the oxidizing agent, a part of the first reducing agent is consumed by the oxygen dissolved in the treated water. Also, the permanganate ion derived from the oxidizing agent can be appropriately reduced. Further, by adding the first reducing agent having 1.3 molar equivalents or less with respect to the oxidizing agent to the treated water, it is possible to suppress an increase in cost due to an increase in the amount of the first reducing agent used.

(Second reduction step)
In some embodiments, after performing the pH adjusting step S4, a second reducing agent may be added to the treated water to perform a second reducing step S8 to reduce the metal element dissolved in the treated water. ..

By adding a second reducing agent to the treated water after the pH adjustment step S4, the metal element dissolved in the treated water can be reduced and converted into another form. For example, by reducing hexavalent chromium dissolved in the treated water to trivalent chromium with a second reducing agent, the treated water can be made easier to handle. An example of a half-reaction formula in which trivalent chromium is produced by reducing hexavalent chromium in the treated water is represented by the following formula (D).
HCrO ₄ ⁻ + 3e ⁻ + 4H ⁺ → Cr (OH) ₃ + H ₂ O… (D)

The second reduction step S8 may be performed at the same time as the first reduction step S6.
Further, the second reducing agent used in the second reducing step S8 may be the same type of reducing agent as the first reducing agent used in the first reducing step S6.

The amount of the second reducing agent added in the second reducing step S8 may be 1.0 molar equivalent or more and 2.0 molar equivalent or less with respect to the oxidizing agent used in the oxidizing step S2.
By adding 1.0 molar equivalent or more of the second reducing agent to the treated water with respect to the oxidizing agent, the metal element dissolved in the treated water can be appropriately reduced. Further, by adding a second reducing agent having 2.0 molar equivalents or less with respect to the oxidizing agent to the treated water, it is possible to suppress an increase in cost due to an increase in the amount of the second reducing agent used.

(Heating process)
In some embodiments, after performing the first reduction step S6, a heating step S10 for heating the treated water may be performed.
By heating the treated water after the first reduction step S6, the fluidity of the precipitate generated by the reaction between the permanganate ion and the reducing agent can be further enhanced. Therefore, it is possible to effectively suppress blockage of piping and equipment caused by sediment.

When the second reduction step S8 is performed, the heating step S10 may be performed after the second reduction step S8 is executed or at the same time as the second reduction step S8.

(Concentration process)
In some embodiments, after performing the first reduction step S6, a concentration step S12 for concentrating the treated water may be performed.
When the treated water after the first reduction step S6 is concentrated, the concentration of the precipitate in the treated water increases. Even in this case, the above-mentioned oxidation step S2, pH adjustment step S4 and first reduction step S6 are performed. Therefore, the fluidity of the precipitate produced in the first reduction step S6 can be maintained relatively high. Therefore, it is possible to suppress blockage of piping and equipment caused by sediment.

The concentration step S12 may be performed at the same time as the heating step S10 described above. Alternatively, the concentration step S12 may include a heating step S10 (ie, the heating step S10 may be performed as part of the concentration step S12). For example, the treated water after the first reduction step S6 may be concentrated by heating (heating step S10 and concentration step S12).
As described above, the treatment efficiency of the treated water can be improved by simultaneously performing the concentration step S12 and the heating step S10, or by performing the heating step S10 as a part of the concentration step S12.

In the concentration step S12, the treated water after the first reduction step S6 may be concentrated using an evaporator. At this time, the treated water may be concentrated while heating the treated water after the first reduction step S6 (heating step S10) using an evaporator (concentration step S12).
As described above, even when the concentration step S12 (and the heating step S10) is performed using the evaporator, the first reduction step is performed by performing the above-mentioned oxidation step S2, pH adjustment step S4 and first reduction step S6. The fluidity of the precipitate produced in S6 can be maintained relatively high. Therefore, the blockage of the evaporator due to the precipitate can be suppressed.

The treated water subjected to the oxidation steps S2 to the first reduction step S6 (and the arbitrarily performed second reduction step S8 to the concentration step S12) is contained in the treated water by passing it through a filter or the like. The deposit may be collected.
Further, the treated water subjected to the oxidation steps S2 to the first reduction step S6 (and the second reduction step S8 to the concentration step S12 arbitrarily performed) is brought into contact with the ion exchange resin to bring about the radioactivity contained in the treated water. The radioactive substance may be removed from the treated water by adsorbing the substance on the ion exchange resin.

Next, the effects of the treated water treatment methods according to some embodiments will be described with reference to Test Examples.
(Test Example 1)
_3. 30 mg of chromium (III) oxide (Cr ₂ O ₃ ) was mixed with 20 L of pure water simulating the water in the primary cooling loop 10 of the nuclear plant 1, and potassium permanganate (KMnO ₄ ) was used as an oxidizing agent. 0 g was dissolved (oxidation step S2) to obtain treated water 1 for testing.
Next, 1.0 g of sodium hydroxide (NaOH) was added to the test treated water 1 as a pH adjuster and stirred (pH adjustment step S4). When the pH of the treated water for test 1 was measured, it was pH 11-12.
Next, 395 mg / L of sodium bisulfite (NaHSO ₃ ) (1.2 molar equivalents with respect to KMnO ₄ , which is an oxidizing agent) was added to the treated water 1 for testing as a reducing agent, and the mixture was stirred (first reduction step S6). ), A precipitate was formed. When the test treated water 1 containing this precipitate is tilted together with the container, the precipitate is deformed so as to collect in the lower part of the container according to the shape of the container at a position tilted by at least 70 ° from the initial position. It was visually confirmed (ie, deformed by gravity).
Next, the test treated water 1 containing the precipitate was concentrated at 100 ° C. until the volume of the test treated water 1 became 1/100 to 1/360 (heating step S10 and concentration step S12). When the test treated water 1 containing this precipitate is tilted together with the container, the precipitate is deformed so as to collect in the lower part of the container according to the shape of the container at a position tilted at least about 20 ° from the initial position ( That is, it is visually confirmed that it is deformed by gravity).

(Test Example 2)
Test Example 2 is different from Test Example 1 in that the type of oxidizing agent used and the pH adjusting step S4 were not performed.
That is, in Test Example 2, 30 mg of chromium (III) oxide (Cr ₂ O ₃ ) was mixed with 20 L of pure water simulating the water in the primary cooling loop 10 of the nuclear power plant 1, and permanganate (permanganate) was used as an oxidant. A solution of HMnO ₄ ) was added to obtain treated water 2 for testing at 150 mg / L. When the pH of this test treated water 2 was measured, it was pH 2 to 3.
Next, 395 mg / L of sodium bisulfite (NaHSO ₃ ) (1.2 molar equivalents with respect to the oxidizing agent HMnO ₄ ) was added to the test treated water 1 as a reducing agent and stirred, and a precipitate was formed. .. When the test treated water 2 containing this precipitate was tilted together with the container, it was visually confirmed that the precipitate did not deform (that is, did not deform due to gravity) even if it was tilted by about 70 ° from the initial position. ..
Next, the test treated water 2 containing the precipitate was concentrated at 100 ° C. until the volume of the test treated water 2 became 1/100 to 1/360. When the test treated water 2 containing this precipitate was tilted together with the container, it was visually confirmed that the precipitate did not deform (that is, did not deform due to gravity) even if it was tilted by about 70 ° from the initial position.

Regarding the precipitate formed by adding a reducing agent to the treated water for test, in Test Example 1, the precipitate was deformed at a position where the container was tilted by about 70 °, whereas in Test Example 2, the container was tilted by 70 °. The precipitate did not deform even when allowed to be allowed to do so. That is, the fluidity of the precipitate after the addition of the reducing agent and before heating and concentration is higher in Test Example 1 than in Test Example 2.
In Test Example 2, the pH was 2 to 3 before the addition of the reducing agent, whereas in Test Example 2, the pH was adjusted to about 11 with a pH adjuster before the addition of the reducing agent, and then the reducing agent was added. Therefore, it is considered that the fluidity of the precipitate produced by the reaction between the oxidizing agent (permanganate ion) and the reducing agent in Test Example 1 became relatively high.

As for the precipitate after heating and concentration, in Test Example 1, the precipitate was deformed at a position where the container was tilted by about 70 °. That is, in Test Example 1, the fluidity of the precipitate after heating and concentrating the treated water for test is higher than that before heating and concentrating. As a result, it was confirmed that the fluidity of the precipitate can be further increased by heating and concentrating the treated water after the precipitate is formed.

Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and includes a modified form of the above-described embodiments and a combination of these embodiments as appropriate.

In the present specification, expressions representing relative or absolute arrangements such as "in a certain direction", "along a certain direction", "parallel", "orthogonal", "center", "concentric" or "coaxial". Strictly represents not only such an arrangement, but also a tolerance or a state of relative displacement at an angle or distance to the extent that the same function can be obtained.
For example, expressions such as "same", "equal", and "homogeneous" that indicate that things are in the same state not only represent exactly the same state, but also have tolerances or differences to the extent that the same function can be obtained. It shall also represent the state of existence.
Further, in the present specification, the expression representing a shape such as a quadrangular shape or a cylindrical shape not only represents a shape such as a quadrangular shape or a cylindrical shape in a geometrically strict sense, but also within a range in which the same effect can be obtained. , The shape including the uneven portion, the chamfered portion, etc. shall also be represented.
Further, in the present specification, the expression "comprising", "including", or "having" one component is not an exclusive expression excluding the existence of another component.

1 Nuclear Plant 2 Reactor 4 Steam Turbine 6 Generator 10 Primary Cooling Loop 11 Reactor Container 12 Fuel Rod 13 Control Rod 14 Pressurizer 15 Pump 16 Steam Generator 18 Primary Coolant Pump 19 Reactor Condenser 20 Secondary Cooling Loop 21 High-pressure turbine 22 Low-pressure turbine 23 Moisture separation heater 24 Condenser 25 Condensation pump

Claims (11)

An oxidation step in which a decontamination object to which a metal oxide is attached is immersed in treated water containing permanganate ions derived from an oxidizing agent to elute the metal elements constituting the metal oxide into the treated water.
A pH adjusting step of adding a pH adjusting agent to the treated water after the oxidation step to adjust the pH of the treated water to 7 or more and 13 or less.
A first reducing step of adding a first reducing agent to the treated water after the pH adjustment step to reduce the permanganate ion contained in the treated water to form a manganese-containing precipitate .
A decontamination-treated water treatment method, which comprises. The decontamination-treated water treatment method according to claim 1, further comprising a heating step of heating the treated water after the first reduction step. The decontamination-treated water treatment method according to claim 1 or 2, further comprising a concentration step of concentrating the treated water after the first reduction step. The decontamination-treated water treatment method according to claim 3, wherein the concentration step includes a heating step of heating the treated water after the first reduction step . The decontamination-treated water treatment method according to any one of claims 1 to 4, wherein in the pH adjusting step, the pH of the treated water is adjusted to 10 or more and 12 or less. The decontamination-treated water treatment method according to any one of claims 1 to 5, wherein the oxidizing agent contains potassium permanganate. The decontamination-treated water treatment method according to any one of claims 1 to 6, wherein the pH adjuster contains at least one alkali metal hydroxide. The decontamination-treated water treatment method according to any one of claims 1 to 7, wherein the first reducing agent contains at least one of hydrogen sulfite, sulfite, and hydrazine. The first reducing step according to claim 1 to 8, wherein the first reducing agent having 1.1 molar equivalents or more and 1.3 molar equivalents or less is added to the treated water with respect to the oxidizing agent. The decontamination treatment water treatment method according to any one item. Claims 1 to 9 further include a second reducing step of adding a second reducing agent to the treated water after the pH adjusting step to reduce the metal element dissolved in the treated water. The decontamination treatment water treatment method according to any one of the above. The removal according to claim 10, wherein in the second reducing step, a second reducing agent having 1.0 molar equivalent or more and 2.0 molar equivalent or less is added to the treated water with respect to the oxidizing agent. Dyeing treatment water treatment method.

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